#include <stdio.h>
int main()
{
	float a,b,c,s,area;
	printf("Input a,b,c:");
	scanf("%f %f %f", &a, &b, &c);
	s=(float)(a + b + c) / 2;
	area=sqrt(s * ( s- a ) * ( s - b ) * ( s - c));
	printf("area=%f\n", area);
	
	return 0;
}